JPS60100734A - Device for testing optical shape of specular surface - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Industrial applications: The present invention relates to an apparatus for testing optical surfaces.

Conventional technology: During interferometric trials to determine whether optical reflective ammonium meets design criteria, zero collector
It is often necessary to use correct, or ) Y. When using an interferometer as a test device, this means that the wavefront reflected from or transmitted from the optical element under test has a wavefront that combines with the reference beam and measures the degree of deviation of the test surface from the desired surface shape. It is necessary to form a directing stripe pattern as much as you require. - During implementation, the zero collector introduces a test beam with an aberration complementary to the shape of the test surface, each beam hitting or leaving the test surface perpendicularly and interfering with the reference wavefront to produce the desired wavefront. A perfect or nearly perfect wavefront is obtained that can form a striped pattern.

Problem to be Solved by the Invention: Zero collectors to date have used various combinations of lenses whose complexity increases as the complexity of the shape of the test surface increases. For large aspheric mirrors, such as the main mirror of a space telescope, the design and manufacture of lens-shaped zero collectors is extremely difficult and prohibitively expensive. When testing conical or Axicon type surfaces of the Walter type I, N or ■, it is almost impossible to design a suitable zero-brick assembly, especially if the refractive power is high.

SUMMARY OF THE INVENTION According to the present invention, a single circularly scored grid is used in place of the multiple lenses required to form a well-designed zero collector. An interferometric system is obtained that attempts to match the shape to that of the design surface, thereby solving the problem.

The light beam from the working radiant light source is directed through a circularly scored grid onto the test surface. The grating lines are unequally spaced according to known design standards so that each beam of light, upon reflection or transmission, forms a striped pattern indicating the deviation of the shape of the test surface from the desired shape. It is ensured that a perfect or nearly perfect wavefront is formed suitable for combination with the wavefront. The stripe pattern recording can be made so that the test surface can be further processed until the design criteria are met.

Embodiment: In FIG. 1, a circularly scored grid 11 is shown. If the intervals between the lines on the circularly scored grating 11 are equal, then the exposed grating placed in the converging beam will have a linear axicon of $ 1Rj+L, that is, the grating will be defined by the following known grating equation from the rays of the rays to the fine ones. Diffract to converge on the ring: sin il − sin i = mλF (1) where 1 and 11 are the angles between the incident light and the diffracted light and the normal to the surface, respectively, m is the diffraction order, λ is the wavelength, and F is the lattice frequency. However, when the image is exchanged with an object, the ring becomes a regular divergent beam of light.

However, if a circular grating is scored with a linear change in frequency according to This is the half-value direction position of the line. Equation (2) is, of course, an equation for a single lens.

If the ruled lines on the grating are unequally spaced apart by a power polynomial: Higher order wavefront errors or aberrations are introduced. Even in the absence of physical spacing, one light exposure is allocated to one wave of OPD per grid line, as in the case of a linear grid.

To obtain , the frequency expression is integrated from the chief ray radius (rp ) to the intersection radius, in which case the rays hitting the center of the grating are not scattered.

The grating frequency Fr at an arbitrary radial position r in FIG. 1 can be expressed by the polynomial of equation (6). The most significant vectors for the lattice are the normal p1 to the line connecting the lattice center with the intersection point, the tangent q to the score line, and the normal r to the lattice. For a ray of light traveling in the direction of unit vector S, the m-th order diffraction has the maximum intensity in the direction of Sl according to the following equation: n's'
xr=nsXr-1-(mλFr)q (4) where n and n' are the refractive indices before and after the grating, respectively. A ray of light traveling in the meridional plane is bent according to the lattice equation abbreviated to li: n'sin i' = n sin
i +mλFr (5) Although FIG. 1 shows a transmission grating, the above analysis applies equally well to reflective gratings.

Furthermore, the analysis shows that nonuniformly spaced gratings can be designed to generate pyro wavefronts for various optical systems, such as axicon elements, aspheric surfaces, and conical segments.

FIG. 2 shows an interferometer for testing the surface shape of an axicon ring mirror. Interferometer zero collector arm 1 consisting of zero collector T-arm 13 and original interferometer 14
3 is Axikonri/Gumira-15χ having a surface of 15ay.
Be prepared. Axicon ring mirror 15 shown in -1fT plane
is an annular ring concentric with the optical axis of the system. ring mirror 1
The surface of 5 is not a through-plane, but has a surface according to the following term in equation (6). Furthermore, the zero collector arm 13 has a reflective circular ruled grating 16 and a convex spherical mirror 17 arranged concentrically with the optical axis of the system. Is the grid 16 a center hole? and the spherical mirror 11 is arranged to reflect the light ii#J'& from and to the axicon ring mirror 15 through the grating 16. Spherical mirror 17 and reflection grating 16
is useful for testing the surface of an axicon ring mirror as long as it is illuminated at a wide enough angle to illuminate the surface of the axicon with a relatively large diameter.

The spherical mirror 17 and the grating 16 are adjusted for spacing, inclination and center position before being set on the axicon link mirror 15i and the zero collector arm 13. The original interferometer 14 is placed in a coaxial reference arrangement, i.e. its center is placed on the optical oil. mirror 1
8, but other types of interferometers such as Tw
It is pointed out that the yman-Green form should be used.

The beam splitter 20 is arranged coaxially with the reference mirror 18.

Rade light source 19 For example, HeNθ laser beam splitter 2
0 and a reference mirror 18 to direct the beam. The mirror transmits half of the light i1Y and reflects half of it. A portion of the wavefront reflected by the reference mirror 18 is reflected by the beam splitter 20 onto the surface 21 as a reference beam f or wavefront.

A part of the luminous flux transmitted through the glue mirror 18v enters the pyrocollector arm 13 and is reflected by the spherical mirror 1T and the reflection grating 16 onto the surface 15eL of the axicon ring mirror 15. The beam is then reflected back to the grating 16 and the spherical mirror 1T, from where it is transmitted as a complete wavefront to the light splitter 20. The beam splitter 20 converts this wavefront into a surface 21
There, this wavefront interferes with the reference wavefront reflected from the reference mirror 18, forming a striped pattern. This striped pattern is the test surface, in this case the axicon ring mirror surface 15a.
The surface 21 is an indicator of the deviation from the desired shape of the videcon or PM knee r! or any other device screen that permanently records the striped pattern, which can be used by the technician to correct imperfections in the shape of the test piece 15a.

Since the type and shape of the surface is determined by the grid spacing, this spacing must be carefully designed.

Different gratings must be designed and manufactured for each surface of the lens-shaped zero collector.

An example of a lattice design for a given axicon surface is shown below.

For an axicon with a surface determined by the following parameters: x =' aY +bY2-1- aY3-1- aY
'[Here Y=M-215,9'mm, a=-0,7
687131, b = -2,6925678-6, C
= -5,3934838-6, (L = -9,984
It is 4060-9. ] The lattice parameters up to the 7th order of the polynomial in equation (6) are Fo = 364.5158, F1 = -33,46055
, F2 = 2.406959, y3 = -7,165
9916-2, F4=1.051 7768-3, Fa
= -7,7675566-6, F6 = 2.297
It is 550-8. The scale is 260 mm to inches.

For every surface given surface parameters, the parameters of the position grid can be determined, for example, by a suitably programmed computer.

FIG. 6 shows the zero collector arm measuring the aspherical surface 310. In this case, the circular ruled grating 32 is of a transmissive type, ie the light beam passes through the grating as opposed to being reflected from the grating in the sampling device of FIG. The zero collector arm in FIG. 6 is replaced with the zero collector arm 13 in FIG. A striped pattern representing the deviation between the aspherical surface and the desired surface shape of the aspheric surface can be formed.

The lattice 32 has the polynomial (6) and the aspherical equation: [where the variables are known. ] can be used to calculate the distance between the marked lines.

The zero collector arms in Figures 2 and 6 have wavefronts that overlap the gratings.
I must point out that he passes twice. In this case the wavefront entering the interferometer after the second pass is perfect or nearly perfect. This second pass is useful for correcting the beam to remove undesired aberrations, such as those caused by spherical mirror 17. Additionally, the design of the grid must take this two-pass into account.

However, the two passes can be eliminated by in each case combining the wavefront with a reference wavefront before the second pass and re-deflecting the wavefront, for example by means of a mirror, so as to interfere with the reference wavefront.

FIG. 4 shows a zero collector arm for testing the surface shape of a 1Falter mirror or paratheroid segment 41, where the grating 42 is of a reflective type. This zero collector arm of FIG. 4 can be substituted for the zero collector arm 13 of FIG. 2 in order to similarly test and save the surface of the para-alloy r segment 41. The lattice or spacing variation is determined by the polynomial (6) and the known variables that determine the surface of the para Mloy P segment 41.

FIG. 4 shows the wavefront making one pass through the reflective grating.

Moreover, the wavefront reflected from the roseboroy segment 41 does not return to the segment, but reaches the grating 42 and is converted into a complete or almost complete wavefront only by 1& reflected at this grating.

It is thus clear that the irregularly spaced circular ruled grating used in the zero collector arm of an interferometer is a powerful tool for testing the topography of various optical surfaces. A single grating can be used instead of a linear lens-shaped zero collector that is difficult, if not impossible, to design for complex trial surfaces using multiple lenses.

[Brief explanation of the drawing]

1 is a perspective view of a circular engraved grating of the type used in the present invention; FIG. 2 is a diagram of the optical path of an interferometer testing the surface of an axicon whose collector arm contains the grating of the present invention; FIG. is an optical path diagram of the zero collector arm used in the Figure 2 interferometer to test and inspect the surface of an aspherical surface, and Figure 4 is an optical path diagram of the zero collector arm used in the Figure 2 interferometer to test and check the surface of a pararoid segment. 11.16. is an optical path diagram of the zero collector arm.
32.42...Grating 13...Zero collector arm 14...Interferometer 15...Axicon ring mirror 17...Spherical mirror 18...Mirror 19.
... Rede 20 ... Luminous flux splitter 31 ... Aspherical mirror 41 ... Balaporoy 1 segment

Claims (1)

[Claims] 1. A Rede light source emitting 7 beams of light directed toward a reflective surface, a circular ruled grating arranged with respect to the Rede source and the test surface such that each beam of light is reflected from the test surface back to the grating without aberration, and with grooves of such spacing. Has a line. An apparatus for testing the optical shape of a reflective surface, characterized by: 2. The device according to claim 1, wherein the score line intervals are unequal. 6. Apparatus according to claim 2 for determining the cutting interval depending on the desired surface shape of the test surface 4. Reference Lehde light source; Reference Lehde light source and test I! I! ! 4. Apparatus according to claim 3, characterized in that it combines the beams of light reflected from the next surface to generate a striped pattern which is an indicator of the deviation between the shape of the test surface and the shape of the fresh surface. 6. The apparatus according to claim 4, comprising a recording device for recording a striped pattern. 6. The apparatus of claim 4, wherein the grating is of a transmissive type and is located between the laser light source and the test surface. 7. Apparatus according to claim 4, wherein the grating is of a reflective type and is arranged to reflect the light beam reflected from this surface onto the test surface. This is the radius of the marked line. ] Apparatus according to claim 2. 9. The device according to claim 4, in which the interval between the score lines is given by the function Fr=ΣFr" [Fr is the radius of the score line. 10. The distance between the score lines is Function Fr= Σ Fnr” CF
rn=0 is the radius of the scored line. ] Apparatus according to claim 6. is the radius of the marked line. ] Apparatus according to claim 7. 12. A laser light source that emits a beam of light directed toward a reflective surface, a circular ruled grating arranged to reflect this beam of light, and the ruled lines of this grating correct aberrations caused by the test and coating surface of the beam of light reflected from the grating. A device for testing and saving the optical shape of a reflective surface, characterized by having a spacing such that 16. 12th range of % permission request where the interval between the marked lines is different
Apparatus described in section. 14. The apparatus of claim 16, wherein the spacing between the score lines is determined according to the desired surface shape of the test surface. 15. Reference Lase light source; Claim No. 1, comprising a device that combines the reference Lase light source and the light flux reflected from the test surface to generate a striped pattern that is an indicator of the deviation between the shape of the test surface and the shape of the desired surface. The device according to item 14. 16. The apparatus according to claim 15, comprising a recording device for recording a striped pattern. 1Z A light source of colorless light directed toward the test surface, with a circular ruled grating arranged so as to reflect or transmit each beam of light through the test surface as an almost complete wavefront, and with respect to the light source and the test surface. An apparatus for testing the optical shape of a reflective surface, characterized by having a score interval of 18. The device according to claim 17, wherein the score line intervals are unequal. 19. The device according to claim 18, wherein the grid spacing is determined depending on the surface shape of the test surface.